javascript 高效的textarea字数监控

<input type="text" name="textfield" id="text_input" />
<div>您输入的值为：<span id="test">还未输入</span></div>

<script type="text/javascript">
function immediately(){
  var element = document.getElementById("text_input");
  if("\v"=="v") {  //IE 6 7 8
    element.onpropertychange = webChange;
  }else{
    element.addEventListener("input",webChange,false);
  }
  function webChange(){
    if(element.value){document.getElementById("test").innerHTML = element.value};
  }
}

immediately();
</script>